You can easily change your data plan, activate, and remove lines at no extra cost to you. There are some instances where your credit card will be charged immediately, including:
Data Packs: 1GB top-ups available for $15. Data Packs can be add a la carte or automatically in 1GB increments.
International Roaming: Cost of data (value established at the setup of the trip), voice and text ($10)
International Calling: $5 monthly service activation fee added to your wallet, an additional $5 credit top-up once your balance falls below $2.